Radeon 9550 problem

I just got a brand new ATI Radeon 9550 AGP 4x/8x card 256 MB. I enabled AGP in the BIOS and installed the newest drivers from nVIDIA for my chipset. When I start my system up there's no problem and I get all the way to the WinXP bootscreen. But then I get a 'no signal' message and the screen goes blank. My system itself keeps running. I know it's not my flat panel monitor since it works fine with my ATI Radeon PCI card. I also tried a DVI cable but with the same result.
My motherboard doesn't have integrated video so I'm a bit reluctant to uninstall my PCI card at this time. Or could that be the problem? In the BIOS I set my initial Video to Onboard/AGP when I try to get the AGP card to work.
Does anyone have a solution?

Had to buy my own graphics card and bought an ATI Radeon 9250 PCI 128 MB.
But I got the problem fixed now. Downloaded newest drivers from ATI and uninstalled both graphics cards and drivers. Left only AGP card in my computer, rebooted and installed new drivers. Graphics work now and no more black screen. Thanks for the help!